The present invention relates generally to satellites, and more particularly, to systems and methods that raise the orbit of a satellite using variable thrust produced by electric propulsion thrusters
The assignee of the present invention manufactures and deploys spacecraft that orbit the earth. Heretofore, numerous efforts have been made to determine the optimum electric orbit raising profile with a fixed thrust level. These efforts include SEPSPOT and HYTOP simulations, for example known to those skilled in the art. Hughes has used electric orbit raising with fixed thrust on their 702 satellites. The Deep Space 1 satellite has used a variable thrust electric thruster in a non-orbit raising application for power management, but not to increase payload mass.
Prior art has generally used fixed thrust levels for orbit raising. Some prior art has considered the use of variable thrust levels to optimize the power profile for non-orbit raising electric missions. No prior art has considered how one may use variable thrust levels during orbit raising specifically to increase payload mass delivered in electric orbit raising. It has been determined by the present inventor that, with throttling, the effective mass benefits of electric orbit raising can be increased by about 25%.
Therefore, it would be advantageous to have improved systems and methods that raise the orbit of a satellite into orbit. It would also be advantageous to have improved systems and methods that use variable thrust levels in electric orbit raising to optimize the payload mass delivered into orbit.
To meet the above and other objectives, the present invention provides for systems and methods that use variable thrust levels in electric orbit raising to optimize the payload mass delivered into orbit. Electric orbit raising uses electric propulsion for satellite orbit raising. In general, electric orbit raising allows the delivery of more payload mass into orbit in exchange for additional orbit raising time. The present invention further increases the payload mass that can be delivered using electric orbit raising without increasing the time or power needed for the satellite to reach orbit.
An exemplary method 30 comprises a method to launch a satellite into orbit that optimizes the mass of the satellite delivered into orbit. The method comprises the following steps. A satellite carrying one or more chemical propulsion devices and one or more electric propulsion devices 16 is launched into a transfer orbit using a launch vehicle. A selected one of the chemical propulsion devices is fired to raise the orbit of the satellite from the transfer orbit to an intermediate orbit. One or more of the electric propulsion devices is fired to raise the orbit of the satellite from the intermediate orbit to final geosynchronous orbit, wherein the one or more electric propulsion thrusters are throttled to produce variable thrust levels so that they operate at an optimum specific impulse level to optimize the mass of the satellite delivered into orbit.
Exemplary systems comprise a satellite including an on-board computer. One or more solar arrays, a communication link, one or more chemical propulsion devices, and one or more electric propulsion devices. A launch vehicle is used to lift the satellite from the earth into a transfer orbit. A ground station having a computer and a communication link is used to communicate with the satellite.
A computer program is preferably employed either in the satellite or at the ground station that fires a selected one of the chemical propulsion devices to raise the orbit of the satellite from the transfer orbit to an intermediate orbit. The computer program is then used to fire a selected set of the electric propulsion devices to raise the orbit of the satellite from the intermediate orbit to final geosynchronous orbit. The computer program is operative to throttle the one or more electric propulsion thrusters to produce variable thrust levels so that they operate at an optimum specific impulse level to optimize the mass of the satellite delivered into orbit.
The computer program may be located in the on-board computer and operates without substantial ground control. Alternatively, the computer program may be located at the ground station and operates under control from the ground station. Alternatively, control commands that fire the thrusters may be manually generated at the ground station and uplinked to the satellite under operator control.